In 1856, a shipment from London, England, to the colony of British Guiana was delayed. The ship was carrying stamps. To stave off a shortage, the local postmaster had the printers at a local newspaper run off a small batch of temporary stamps. The printers made three types, says the Associated Press, a 1-cent stamp and a 4-cent stamp in magenta, and a 4-cent stamp in blue.
Since they were just temporary stamps, says the AP, “the postmaster ordered that the stamps be initialed by a post office employee,” a way to ensure their legitimacy. The stamps were nothing special.
Over time, however, the 1-cent magenta stamp, in particular, has skyrocketed in value—there is only one known copy left in existence, and as a bonus, the stamp's former owners have an eclectic history, which the AP details. For the past 141 years, the stamp has been bouncing around from collector to collector, being sold privately or at auction for ever-increasing sums.
Now, says the AP, the 1-cent magenta stamp is going up for auction on June 17. It is expected to net somewhere between $10 and $20 million, a sum that would smash the record for the most valuable single stamp in existence.
According to the wonderful Money chart by xkcd author Randall Munroe, the 1-cent magenta stamp is literally worth more than a human life, as defined by the EPA.